This invention relates to the field of plant breeding, stress tolerance and plant transformation methods. More specifically, transgenic turfgrass is provided, which is salt and drought tolerant by virtue of expressing a transgene encoding betaine aldehyde dehydrogenase.
Various scientific and scholarly articles are referred to in parentheses throughout the specification. These articles are incorporated by reference herein to describe the state of the art to which this invention pertains.
Environmental stress is one of the most important factors limiting turfgrass growth and survival. Drought and soil salinity are two of the foremost environmental problems. As world population increases, the acreage of turfgrasses expands also. Turfgrass is used in almost all recreation and athletic fields. Because of limited cultivable lands, more turfgrass acreage has been developed in arid or semiarid regions where soil and water salinity are always a problem for plant growth. In recent years, more and more turfgrass stands are cultivated near bodies of salt water, for example, seaside golf courses. The use of salts for deicing highways, sidewalks and airport runways is another example of increasing soil salinity. Thus, increasing environmental stress tolerance, especially drought and salt tolerance, has been one of the major objectives in turfgrasses breeding programs.
Under drought or salt stress, glycine betaine is accumulated in cells of some higher plants and animals as an osmoprotectant (Hanson and Grumet, 1985, In Cellular and Molecular Biology of Plant Stress, ed. J. L. Key, T. Kosuge, pp.71-92, New York: Alan R. Liss, Inc.). Its possible physiological functions, biosynthetic pathways and synthesis-related genes have been studied (Rhodes, 1993, Annu. Rev. Plant Physiol. Plant Mol. Biol. 44:357-384; McCue and Hanson, 1990, TECH 8:358-62). Recently, glycine betaine synthesis-related genes have been isolated (Wrertilnyk and Hanson, 1990, PNAS 87:2745-2749; Xiao et al., 1995, Chinese Science Bulletin. 40(8):741-745; Rathinasabapodhi et al., 1997, PNAS 94:3454-3458). Efforts have been made to increase the activity of betaine synthesis related enzymes through gene transformation in plants in order to increase the glycine betaine accumulation and further improve their drought and salt-tolerance. Transgenic plants of tobacco, rice and strawberry, engineered to overexpress the gene encoding betaine aldehyde dehydrogenase (BADH), have shown improvement in salt tolerance (Holmstrom et al., 1994, The Plant J. 6(5):749-758; Liu et al., 1997, Acta Genetic Sinica. 24(1):24-28; Guo et al., 1997, Science in China 40:496-501). However, no turfgrass as yet has been engineered to overproduce BADH, and so improved salt tolerance in turfgrass has not been achieved by this mechanism. Inasmuch as each genus of plant, especially monocotyledonous plants (which have proven more recalcitrant to tissue culture, regeneration and transformation than dicotyledonous plants), has its own specific requirements for transformation and/or regeneration, it is of significant agronomic and economic importance to develop an efficient turfgrass transformation system, and further to generate salt tolerant turfgrass species using such a system.
The invention provides transgenic turfgrasses having increased salt tolerance by virtue of expressing a gene involved in the biosynthesis of glycine betaine, an osmoprotectant.
According to one aspect of the invention, a transgenic cell of a Graminaceous plant is provided, which comprises a transgene encoding an enzyme of the glycine betaine biosynthetic pathway. In a preferred embodiment, the transgene encodes betaine aldehyde dehydrogenase from Atriplex hortensis, and in a most preferred embodiment, plasmid pRTT120 comprises the transgene. The transgenic cell is preferably a turfgrass, and most preferably selected from the group consisting of Creeping Bentgrass, Perennial Ryegrass, Kentucky Bluegrass, and Bermudagrass.
A salt-tolerant Graminaceous plant produced from the aforementioned transgenic cell is also provided. Preferably, this salt-tolerant turfgrass is also drought-tolerant. Seeds produced from the salt-tolerant turfgrass are also provided.
According to another aspect of the invention, a salt-tolerant transgenic Graminaceous plant is provided which expresses a transgene encoding an enzyme of the glycine betaine biosynthetic pathway. Preferably, the plant expresses a transgene encoding betaine aldehyde dehydrogenase from Atriplex hortensis, and most preferably pRTT120 comprises the transgene.
The salt-tolerant transgenic Graminaceous plant is also preferably drought-tolerant, and preferably is selected from the group consisting of Creeping Bentgrass, Perennial Ryegrass, Kentucky Bluegrass and Bermudagrass. Seeds of the transgenic plant are also provided.
Another aspect of the present invention is a transgenic Graminaceous plant with improved phenotypic characteristics. This transgenic plant has at least one of the following characteristics: higher BAH activity, a higher concentration of glycine betaine and a higher growth rate under salt stress, and a higher level of drought tolerance.
Other features and advantages of the present invention will become apparent from the drawings, detailed description and examples that follow.